Shock absorber in elastomer material for a suspension connecting rod or other connecting component

ABSTRACT

This invention pertains to an absorber in elastomer material for a connecting component, such as a connection rod, the said component having a head with two faces parallel to each other and traversed by a bore forming a housing for a ball-joint with its cage. The absorber is characterised in that it has two elements in the form of discs, parallel to each other, each with a central opening sufficiently wide so as not to cover the portions of the ball-joint protruding in relation to the head and connected at their periphery by means of connection. The present invention is applied in particular to suspension connecting rods installation of the accessories gearbox of a turbojet.

The present invention pertains to a shock absorbing element for a connecting component, such as a connecting rod, with a flat head, mounted via a ball joint to a pin which is integral with a female yoke. The function of the element is to absorb vibrations between the head and the yoke. The particular use of this invention is for a suspension connecting rod for a module such as the housing enclosing the gears for driving accessory machines on a gas turbine engine applied to the aviation field.

A gas turbine engine used for the propulsion of aircraft, a turbojet in particular, includes accessory machines necessary for its operation. Examples are fluid pumps for actuating the control, lubrication or fuel components and also electrical generators. These machines are installed mechanically driven by a gearbox which is itself connected to an engine shaft by a suitable mechanical link. The gearbox is designated by common accord by its abbreviation, AGB for “Accessory Gear Box”, in the field concerned. The gearbox is maintained in suspension on the engine housing slightly downstream of the impeller stage by connecting rod-shaped connecting components.

A connecting rod consists of a rod ending at its two ends by a head of flat shape, with two parallel faces, in the bore of which an externally cylindrical cage is maintained by crimping. The internal surface of the cage acts as a guide to a sleeve with a spherical exterior surface forming a ball-joint. A self-lubricating cloth is glued to the inside of the cage which remains in contact with the spherical surface of the ball-joint to enable relative movements therebetween. This cloth enables the vibration phenomena to be absorbed by an assembly without play and with swivelling torque.

Each connecting rod head 10 is mounted between the lugs 21 and 23 of a female yoke 20 as shown in FIG. 1. In that figure one cannot see the entire connecting rod, only a portion of the head. The head includes two faces parallel to each other 11 and 12, pierced by a bore for the cage housing 13 with its ball-joint 14. The self-lubricating cloth is not shown. The head is maintained between the two lugs of the yoke by a screw 30 which passes through the lugs and the ball-joint. The screw is itself immobilised by a nut 33.

The connecting rod is immobilised axially depending on the direction of the screw 30 by the ball-joint which, as one can see in the figure, is pressing on one side against the internal face of the yoke lug 23 and on the other side against a shoulder 35 of the screw. As a result of this assembly with the ball-joint, the connecting rod head can pivot freely around the screw axis and around any axis perpendicular to the screw axis within the limits of the stops defined by the environment. The movement is limited in particular by the clearance existing on either side between the connecting rod head and the yoke lugs.

During the life-time of the engine, this link is subject to micro-movements due to vibration forces, in particular to stresses orientated parallel to the screw axis, due in particular to the low inclination of the connecting rods compared to the horizontal plane. These stresses in the long term end by wearing and degrading the self-lubricating cloth between the ball-joint and the cage. There follows contact and damage to the metal surfaces which necessitate a repair operation.

The intention of the present invention is to perfect a means of absorbing vibration between the connecting rod head and the lugs of the yoke in which it is mounted.

More generally the purpose of the invention is a means of absorbing vibration between a connecting component installed with a ball-joint between the two lugs of a yoke.

Sliding washers in elastomer material were proposed between the face-to-face surfaces of the connecting component head and the yoke. However, such an assembly is not easy since it is difficult to maintain the washers in place before assembling the screw while ensuring that they are centred. The technician has little space around the engine when the repair must be carried out under the aircraft wing, that is to say, outside the workshop. To resolve this problem, it was proposed to glue the washers on the faces of the connecting component head. However, this solution did not appear satisfactory since the adhesive inserts itself between the ball-joint and the cage causing degradation to the swivelling function.

The purpose of the invention is therefore a means of absorption for the connecting component which is simple to apply and which causes a significant increase in the life-time of the swivelling assembly.

In conformity with the invention, a shock absorber in elastomer material is produced for a connecting component, such as a connecting rod, the said component having a head with two faces parallel to each other and a bore forming a housing for a ball-joint with its cage, characterised in that it has two elements in the form of discs, parallel to each other, each with a central opening sufficiently wide so as not to cover the portions of the ball-joint which protrude in relation to the head and connected at their periphery by means of connection.

In conformity with another characteristic, the discs have a thickness at least equal to the portion of the ball-joint which protrudes in relation to one face of the head. This arrangement enables a disc to be compressed when tightening the screw in the yoke. During operation, the other disc at least comes also into contact with its adjacent surface and is compressed when the connecting component starts to tilt. This principle provides efficient absorption of vibration and prevents any contact between the head of the connecting component and the yoke lugs.

In conformity with one embodiment, the thicknesses of the two discs are identical.

In conformity with another embodiment, the two thicknesses are different.

Preferably, the said means of connection are formed by a plurality of arms. In particular for the connecting rod heads, they allow for the same absorber to be adapted to several types of geometry and diameters of heads. Where necessary the number and the dimension of the arms would be adapted to the geometry and to the diameter of the connecting component used. This provision enables the absorber to be installed easily, since the two discs can be moved away from each other easily and without effort.

The intention of the invention is also to provide a method to install an absorber on a connecting component, such as a connecting rod, supported by a pin between the lugs of a female yoke. According to this method, since the head of the connecting component is free, the absorber can be slid around the head in such a manner that the two elements in the form of a disc come each against one face of the said head, the head is inserted with the absorber between the lugs of the yoke and the connecting component is locked in the yoke by the said pin.

In accordance with one particular embodiment, since the clearance between each face and the adjacent lug is different and the absorber having one element thicker than the other, the thicker element is placed between the face and the lug which has the largest clearance.

The intention of the invention is also to provide an absorbing system for a connecting component installed on a yoke with two lugs having an absorber such as presented above between each face and the lug which faces it.

Now the absorber of the invention will be described in more detail with reference to the drawing in which

FIG. 1 shows the installation of a connecting component on a yoke in conformity with the prior art.

FIG. 2 shows in perspective an absorber in conformity with the invention,

FIG. 3 shows the absorber mounted on a connecting rod head,

FIG. 4 shows in axial section the installation of the absorber of the invention.

Referring to FIG. 2, one sees the absorber of the invention before installing on the connecting component head. The absorber 100 consists of a first part 101 and a second element 103 in the form of discs. These two elements 101 and 103 have a central circular opening, 101′ and 103′ respectively. They are connected one to the other at their periphery by axial connection means, here by six arms 110, 111, 112, 113, 114 and 115 which maintain them at a determined distance. The arms are arranged so as to enable the absorber to be installed on the head of the connecting component. Preferably, the elements and the connecting means have come from the mould in the same material. The latter is an elastomer the chemical composition of which is suitable for the filtering function of vibration but also for the environment in which it is placed. For example, it can be necessary to provide resistance to chemical aggression, to oil and kerosene and to the various temperature conditions to which the absorber is subject during operation and when not in operation. For the application to the suspension of the AGB gearboxes of a turbojet, a fluorosilicone based elastomer would be suitable.

The absorber is shown in FIG. 3 in place on the head of the connecting component before the latter is installed on the yoke. The absorber has been slid onto the head like a sock, in accordance with the direction of installation indicated. The elements 101 and 103 are each applied on a face 11 or 12 of the head 10. The arms 110 to 115 maintain in place the two elements on the head. It was observed that the orifices 101′ and 103′ are sufficiently wide so as not to cover the portions of the ball-joint protruding on either side of the head 10. Further, the thicknesses of the elements 101 and 103 are sufficient so that the ball-joint 14 does not protrude compared to the planes of elements 101 and 103.

In FIG. 4, the connecting rod head is shown mounted on the yoke as in FIG. 1 but this time it is provided with the absorber. Compared to FIG. 3 the two elements are slightly compressed between face 11 and lug 21 on the one hand and face 12 of head 10 and lug 23 on the other hand. The thickness of each of the elements has been chosen depending on these two plays.

For example for a connecting rod mounted on a yoke with a play of 1.7 mm on one side, and higher than the thickness of the disc on the other side, one has chosen two elements of the same thickness of 2 mm.

Endurance tests were carried out on the AGB gearbox rear suspension connecting rods. No change was found in the mechanical and dynamic behaviour of the suspension and therefore in its vibration endurance capacity. The insertion of the absorbers does not modify the technical definition of the pieces which provide the structural strength of the suspension. Consequently the engine vibration indications remain unchanged.

On the other hand, the vibration situation of the suspension connecting rods develops positively and significantly which is translated into a consequent increase in the life-time of the swivelling assembly.

Partial comparative vibration endurance tests between a connecting rod A without absorber and a connecting rod B with absorber were conducted to demonstrate the efficiency of the absorption.

The test conditions are as follows:

The fastening of the connecting rods was representative of the fastening on the engine: yoke, pins, nuts.

Two endurance tests were conducted:

-   -   one endurance test during 5×10⁷ cycles at a frequency of 2000 Hz         with an acceleration of 25 g, applied in the axial direction of         the ball-joint,     -   one endurance test during 7.2×10⁷ cycles on the connecting rod         natural frequency on the 1F mode (1200 Hz) at an acceleration of         level 25 g, applied in the axial direction of the ball-joint.

The results of the tests are as follows: for A one finds start of wear of the ball-joint translated into a loss of rotation torque due to degradation of the self-lubrication cloth under the effect of micro-movements, and a start of play occurring between the ball-joint and its cage. For B one finds absence of any change in the mechanical behaviour of the ball-joint throughout the endurance test. These results show that the resistance of the suspension connecting rods to vibrating endurance is not degraded but is significantly improved. 

1) Absorber in elastomer material for a connection component, such as a connecting rod the said component having a head with two faces parallel to each other and traversed by a bore forming a housing for a ball-joint with its cage, characterised in that it includes two elements in the form of discs, parallel to each other, each with a central opening sufficiently wide so as not to cover the portions of the ball-joint which protrude in relation to the head and connected at their periphery by means of connection. 2) Absorber according to claim 1 the elements of which in the form of discs have a thickness at least equal to the portion of the ball-joint which protrudes compared to one face of the head. 3) Absorber according to claim 1 where the thicknesses of the two elements are the same. 4) Absorber according to claim 1 where the thicknesses of the said two elements are different. 5) Absorber according to claim 1 where the said means of connection are formed by a plurality of arms. 6) Method for mounting an absorber according to claim 1 on a connecting component, such as a connecting rod, supported by a pin between the lugs of a female yoke, in accordance with which since the head of the component is free, the absorber is slid around the head in such a manner that the two elements in the form of discs each come up against one face of the said head, the head with the absorber is inserted between the lugs of the yoke and the connecting component is locked in the yoke using the said pin. 7) Method according to claim 6, since the play between each face of the head and the adjacent lug is different, since the absorber has one element thicker than the other, one places the thicker element between the face and the lug which has the largest play there between. 8) Absorption system for a connecting component mounted on a yoke with two lugs having an absorber according to claim 1, between each face of the connecting component and the lug which faces it. 